[PATCH 4/7] mm: use an on-stack bio for synchronous swapin

[Christoph Hellwig]

Optimize the synchronous swap in case by using an on-stack bio instead
of allocating one using bio_alloc.

Signed-off-by: Christoph Hellwig <h...@lst.de>
---
 mm/page_io.c | 69 +++++++++++++++++++++++++++++-----------------------
 1 file changed, 38 insertions(+), 31 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index ce0b3638094f85..21ce4505f00607 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -52,10 +52,9 @@ static void end_swap_bio_write(struct bio *bio)
        bio_put(bio);
 }
 
-static void end_swap_bio_read(struct bio *bio)
+static void __end_swap_bio_read(struct bio *bio)
 {
        struct page *page = bio_first_page_all(bio);
-       struct task_struct *waiter = bio->bi_private;
 
        if (bio->bi_status) {
                SetPageError(page);
@@ -63,18 +62,16 @@ static void end_swap_bio_read(struct bio *bio)
                pr_alert_ratelimited("Read-error on swap-device (%u:%u:%llu)\n",
                                     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
                                     (unsigned long 
long)bio->bi_iter.bi_sector);
-               goto out;
+       } else {
+               SetPageUptodate(page);
        }
-
-       SetPageUptodate(page);
-out:
        unlock_page(page);
-       WRITE_ONCE(bio->bi_private, NULL);
+}
+
+static void end_swap_bio_read(struct bio *bio)
+{
+       __end_swap_bio_read(bio);
        bio_put(bio);
-       if (waiter) {
-               blk_wake_io_task(waiter);
-               put_task_struct(waiter);
-       }
 }
 
 int generic_swapfile_activate(struct swap_info_struct *sis,
@@ -445,10 +442,11 @@ static void swap_readpage_fs(struct page *page,
                *plug = sio;
 }
 
-static void swap_readpage_bdev(struct page *page, bool synchronous,
+static void swap_readpage_bdev_sync(struct page *page,
                struct swap_info_struct *sis)
 {
-       struct bio *bio;
+       struct bio_vec bv;
+       struct bio bio;
 
        if ((sis->flags & SWP_SYNCHRONOUS_IO) &&
            !bdev_read_page(sis->bdev, swap_page_sector(page), page)) {
@@ -456,30 +454,37 @@ static void swap_readpage_bdev(struct page *page, bool 
synchronous,
                return;
        }
 
-       bio = bio_alloc(sis->bdev, 1, REQ_OP_READ, GFP_KERNEL);
-       bio->bi_iter.bi_sector = swap_page_sector(page);
-       bio->bi_end_io = end_swap_bio_read;
-       bio_add_page(bio, page, thp_size(page), 0);
+       bio_init(&bio, sis->bdev, &bv, 1, REQ_OP_READ);
+       bio.bi_iter.bi_sector = swap_page_sector(page);
+       bio_add_page(&bio, page, thp_size(page), 0);
        /*
         * Keep this task valid during swap readpage because the oom killer may
         * attempt to access it in the page fault retry time check.
         */
-       if (synchronous) {
-               get_task_struct(current);
-               bio->bi_private = current;
-       }
+       get_task_struct(current);
        count_vm_event(PSWPIN);
-       bio_get(bio);
-       submit_bio(bio);
-       while (synchronous) {
-               set_current_state(TASK_UNINTERRUPTIBLE);
-               if (!READ_ONCE(bio->bi_private))
-                       break;
+       submit_bio_wait(&bio);
+       __end_swap_bio_read(&bio);
+       put_task_struct(current);
+}
+
+static void swap_readpage_bdev_async(struct page *page,
+               struct swap_info_struct *sis)
+{
+       struct bio *bio;
 
-               blk_io_schedule();
+       if ((sis->flags & SWP_SYNCHRONOUS_IO) &&
+           !bdev_read_page(sis->bdev, swap_page_sector(page), page)) {
+               count_vm_event(PSWPIN);
+               return;
        }
-       __set_current_state(TASK_RUNNING);
-       bio_put(bio);
+
+       bio = bio_alloc(sis->bdev, 1, REQ_OP_READ, GFP_KERNEL);
+       bio->bi_iter.bi_sector = swap_page_sector(page);
+       bio->bi_end_io = end_swap_bio_read;
+       bio_add_page(bio, page, thp_size(page), 0);
+       count_vm_event(PSWPIN);
+       submit_bio(bio);
 }
 
 void swap_readpage(struct page *page, bool synchronous, struct swap_iocb 
**plug)
@@ -509,8 +514,10 @@ void swap_readpage(struct page *page, bool synchronous, 
struct swap_iocb **plug)
                unlock_page(page);
        } else if (data_race(sis->flags & SWP_FS_OPS)) {
                swap_readpage_fs(page, plug);
+       } else if (synchronous) {
+               swap_readpage_bdev_sync(page, sis);
        } else {
-               swap_readpage_bdev(page, synchronous, sis);
+               swap_readpage_bdev_async(page, sis);
        }
 
        if (workingset) {
-- 
2.39.0